A group of seven investigators associated with the Biology, Chemistry, and Brain and Cognitive Sciences Departments of MIT request funds for the purchase of a new JEOL 1200ex transmission electron microscope. This high performance instrument will allow advances in monoclonal antibody technology and genetic engineering to be applied to elucidating the assembly, organization, and function of cell and organelle ultrastructure. The instrument will replace a 17 year old JEOL 100B electron microscope, which is at the end of its life. The major uses of the microscope will be 1) To investigate structural intermediates in the maturation and assembly of viral shells, (Jonathon King); 2) To study the binding to DNA of cis-platinated anticancer agents and proteins recognizing such complexes (Steve Lippard); 3) To study the mechanism by which accessory proteins of microtubules control their assembly and function in different cell types (Frank Soloman); 4) To examine receptor mediated endocytosis of the Low Density Lipoprotein, the major pathway of cholesterol clearance, in mutant mammalian cell lines carrying mutations affecting the LDL receptor (Monty Krieger); 5) To continue the development of new methods for visualizing the cytoskeletal and nuclear frameworks of cultured cells, and to locate specific macromolecule binding sites on the nuclear matrix architecture (Sheldon Penman); 6) To determine the macromolecular anatomy and synaptic location of proteins associated with the development and organization of neuromuscular synapses (Steven Burden), and 7) To investigate the mechanism through which afferent neurons find their target cells in the mammalian central nervous system (Mriganka Sur). The instrument will be housed and administered in the Biomedical Electron Microscopy Laboratory, a multi-user facility serving members of the Depts of Biology, Chemistry, Chemical Engineering, and Brain and Cognitive Science.